Though there are several conventional methods of making zeolitic catalyst compositions, including powder synthesis, many are made commercially through a relatively high solids process by forming an extrudate. For catalyst compositions that experience mechanical stresses, e.g., pressurization in reaction vessels, etc., some mechanical and physical properties of the extrudates can translate to the calcined (activated) catalyst material and can be critical for designing/manufacturing a desired commercial catalyst. Without limitation, these can include crush strength, surface area, density, and L/D. Typically, finished extrudates with low relative L/D ratio and low relative crush strength may cause an excessive pressure drop through the reactor bed. Furthermore, the loading of extrudate (per unit weight or volume) can generally increase dramatically with decreasing L/D. Conventionally for catalyst materials, the inclusion of, or increase in content of, binder could be modified to address mechanical or physical properties of catalyst materials. Another conventional way to deal with less desirable properties includes changing reactor conditions (pressure drop, flux, circulation rate, etc.) to reduce the mechanical stresses on the catalyst materials. However, such changes in reactor conditions can result in significantly lower catalytic and/or product yields, which can be even more undesirable.
Thus, an alternate mechanism for improving certain physical and/or mechanical properties of catalytic materials is sought. In particular, it can be desirable for one or more of crush strength, surface area, density, and L/D to be improved without taking away from catalytic activity. In the description hereinbelow, the use of metal oxides fibers as reinforcement is explored for further improvement in mechanical properties.
Though some short fibers (such as glass fibers) are known as relatively inert fillers, they typically do not provide any additional mechanical stability and can occasionally degrade mechanical properties, particularly if they do not encourage cohesion with the other components of the catalytic material. On the other hand, fibers that are relatively long can provide some additional mechanical strength, but typically only at relatively high loadings, which can then cause problems with extrusion. Therefore, a compromise is sought to attain increased mechanical stability without relatively high loadings of (otherwise inert) reinforcing agents and without significant effect on the catalytic extrudate.